Multiphoton non-local quantum interference controlled by an undetected photon

Kaiyi Qian; Kai Wang; Leizhen Chen; Zhaohua Hou; Mario Krenn; Shining Zhu; Xiao-Song Ma

doi:10.1038/s41467-023-37228-y

Multiphoton non-local quantum interference controlled by an undetected photon

Nat Commun. 2023 Mar 17;14(1):1480. doi: 10.1038/s41467-023-37228-y.

Authors

Kaiyi Qian^#¹, Kai Wang^#², Leizhen Chen¹, Zhaohua Hou¹, Mario Krenn³, Shining Zhu¹, Xiao-Song Ma^{4

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Affiliations

¹ National Laboratory of Solid-state Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China.
² National Laboratory of Solid-state Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China. kai.wang@nju.edu.cn.
³ Max Planck Institute for the Science of Light (MPL), Erlangen, Germany. mario.krenn@mpl.mpg.de.
⁴ National Laboratory of Solid-state Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China. Xiaosong.Ma@nju.edu.cn.
⁵ Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China. Xiaosong.Ma@nju.edu.cn.
⁶ Hefei National Laboratory, Hefei, 230088, China. Xiaosong.Ma@nju.edu.cn.

^# Contributed equally.

Abstract

The interference of quanta lies at the heart of quantum physics. The multipartite generalization of single-quanta interference creates entanglement, the coherent superposition of states shared by several quanta. Entanglement allows non-local correlations between many quanta and hence is a key resource for quantum information technology. Entanglement is typically considered to be essential for creating non-local quantum interference. Here, we show that this is not the case and demonstrate multiphoton non-local quantum interference that does not require entanglement of any intrinsic properties of the photons. We harness the superposition of the physical origin of a four-photon product state, which leads to constructive and destructive interference with the photons' mere existence. With the intrinsic indistinguishability in the generation process of photons, we realize four-photon frustrated quantum interference. This allows us to observe the following noteworthy difference to quantum entanglement: We control the non-local multipartite quantum interference with a photon that we never detect, which does not require quantum entanglement. These non-local properties pave the way for the studies of foundations of quantum physics and potential applications in quantum technologies.